In the image display device in the interlace scanning, for example, the top field image configured by the odd-numbered scanning line and the bottom field image configured by the even-numbered scanning line in the image of one frame are continuously displayed, and are viewed by a person as one image.
Thus, when a composite frame image is just generated from two interlaced field images, there occurs no problem if the images are still images. However, if the images are moving images, the time-lag between the two fields causes the problem of shifted images as afterimages, blurred images, etc. in one composite frame image.
Therefore, in the case of moving images, the field image of one of the top field and the bottom field is generally used in generating a frame image. In this case, it is necessary to obtain by interpolating the data of pixels on every second line in the field image.
FIGS. 1 and 2 are explanatory views of prior art of the method of interpolating the pixel data on every second line in the field image. In FIG. 1, the first and third lines actually have pixels, and the pixel value of the pixel on the second line is interpolated using the pixel values of the pixels on the first and third lines. In the interpolating process, the interpolation value of the central pixel on the interpolation line, that is, the pixel to be interpolated between the pixel of the number 4 on the upper line and the pixel of the number 4 on the lower line, is obtained using the intensity of the pixels of the numbers 0 through 8 on the upper line and the intensity of the pixels of the numbers 0 through 8 on the lower line.
FIG. 2 illustrates examples of the intensity values of actual pixels on the upper and lower lines. Using the intensity values, the absolute value of the difference between the intensity values of the pixels having the similar numbers between the upper and lower lines is obtained. And the average value of the intensity values of the pixels on the upper and lower lines corresponding to the numbers minimizing the absolute value of the difference is defined as the intensity value of the pixel to be interpolated. In FIG. 2, the number minimizing the absolute value of the difference between the intensity values of the pixels on the upper and lower lines is 0. The numbers 0 through 8 indicates the slant of the line connecting the pixel to be interpolated and the pixels of the upper and lower lines of each number. Then, using the slanting line of number 0, the average value of the pixel values of the two pixels of the number, that is, 16, is obtained as the intensity value of the pixel to be interpolated.
FIG. 3 is an explanatory view of the problem of the prior art described above with reference to FIGS. 1 and 2. As illustrated above in FIG. 3, when there is a thin slanting line in one frame image, it may be necessary to interpolate, for example, the data of the pixel on the even-numbered line from the data of the pixel on the odd-numbered line.
As illustrated below in FIG. 3, for example, when the pixel between the pixels of the number 2 on the third and fifth lines is to be interpolated, the absolute values of the differences of the pixel values corresponding to the numbers of the slanting lines are all the same, for example, and the number of the slanting line for the pixel to be interpolated cannot be determined.
Thus, the technology of the prior art of the image conversion system for generating a frame image from a field image is described in the patent document 1. In the patent document 1, the sharpness levels in the even number field and the odd number field are calculated, the interpolating process is performed on the basis of afield at higher sharpness level, the interpolating process is performed on the basis of the even number field, and the interpolating process is performed on the basis of the odd number field depending on the magnitude collation between the absolute value of the difference between the two sharpness levels and the threshold. Then, the intensity values of the interpolation pixels are obtained, and the intensity values are combined and a frame image is generated, thereby generating a high-quality frame image.
Patent Document 1: Japanese Laid-open Patent Publication No. 2004-274361 “Interpolating Method, Interpolating Program, and Record Medium recording the same, for example, and Image Processing Device and Image Forming Device provided with the same, for example”.
However, since the technology of the patent document 1 uses a normal linear interpolation system, the problem described with reference to FIG. 3 does not occur, but the problem of unsmooth jaggy occurs instead. After all, the technology cannot solve the problem that the interpolation on the thin slanting line as described with reference to FIG. 3 cannot be appropriately performed.